If it is an established vine (been there for a while)......you can take off as many leaves as you want.....infact, you can cut the vine off at ground level and it will grow back next year to practically the same height!!!.....You cannot kill this vine.....That is why it is classified as "invasive".....loves the sun....will grow in the shade....rapid grower and once it is established, the root goes down several "feet"...so impossible to remove it.....Hope this helps.....